A phased antenna array system includes a group of antennas being used for signal communication through transmission and reception of electromagnetic waves. In a typical implementation, each antenna is connected to a phase shifter and an amplifier, which control the phase and amplitude of the radiated electromagnetic wave for that antenna. Changing the amplitudes and phases of the signals feeding the array's different antennas leads to changes in the far field radiation pattern of system. The beam of the phased array can therefore be controllably directed.
Precise controlling of the array's amplifiers and phase shifters is important for altering the radiation pattern in terms of power level and beam direction. However, practical considerations, such as physical limitations, environmental conditions and fabrication process variations, impose unwanted errors on the amplitude and phase response of these components, resulting in non-ideal behaviour. Imperfections can also exist in the antenna feed network which is responsible for dividing the input power and distributing signals to antennas. Furthermore, the geometrical parameters such as the location of fabricated antennas are subject to error. Calibration can be used to counteract such imperfections and is considered to be an important part of the operation of a phased array system. Having a priori knowledge about the antennas radiation characteristics, calibration can provide information on various system parameters such as the phase and amplitude response of electrical components and the location of antennas.
Some existing calibration methods are based on changing the value of phase shifters for every single element sequentially, and maximizing the power received (for transmitting mode) or transmitted (for receiving mode) by one or an array of external reference antennas, which are typically located at a distance from the array. The values of phase shifters corresponding to the maximum received (transmitted) powers determine the offset to be applied to each phase shifter and amplifier. Other calibration methods control both the amplitude and phase of the radiated field for every phase shifter or antenna. Through applying the control signal, the phase responses of the array's component antennas are obtained.
However, performing these measurements for an array with large number of antennas can be a time consuming process, particularly because calibration is typically required to be done at least once for each element. Furthermore, from a system identification point of view, existing methods do not provide more detail on other unknown parameters of the system such as the geometrical parameters.
Therefore there is a need for a method and apparatus for phased antenna array calibration, that is not subject to one or more limitations of the prior art.
This background information is provided to reveal information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.